1. Field of the Invention
The present invention generally relates to semiconductor device substrates and, more particularly, to a semiconductor device substrate using a silicon substrate having fine wires formed thereon and a manufacturing method thereof.
2. Description of the Related Art
With high densification of semiconductor devices, the pitch of mounting terminals of semiconductor devices has become smaller. However, since the connection-terminal pad of a circuit board on which a semiconductor device is mounted is formed with a pitch larger than the pitch of the mounting terminals of the semiconductor device, it is difficult to mount the semiconductor device as it is.
Thus, the semiconductor device is mounted on a substrate, which is referred to as an interposer, so as to mount the semiconductor device on a circuit board via the interposer. That is, the electrodes of the semiconductor device are rearranged by the interposer so as to form mounting terminals having a larger pitch, thereby matching with the pitch of the connection-terminal pads on the circuit board.
Generally, the above-mentioned semiconductor device substrate (interposer) has a multilayer structure in which conductive members extend from a surface on which a semiconductor device is mounted to an opposite surface on which mounting terminals are formed. Generally, an organic fine substrate is used for the interposer. In order to obtain finer wiring pattern, a silicon substrate is used in many cases. A multilayer structure is formed by stacking insulating layers and conductive layers on a silicon substrate. The conductive member that penetrates an insulating layer can be easily formed by a through hole such as a plated via hole of a build-up substrate. A silicon substrate has a relatively large thickness so as to maintain a strength as an interposer. Therefore, a special fabrication process is needed so as to form the conductive members that extend in a direction of the thickness with a fine pitch.
An approach as one method of forming the conductive member that extends through a silicon substrate will be explained below.
First, a thick silicon substrate is prepared, and holes having a thin cylindrical shape are formed in the silicon substrate in the same arrangement as mounting terminals. Each hole having the thin cylindrical shape is referred to as a blind via that extends to the middle of a silicon substrate. After forming an insulating film on an inner surface of each hole, a metal is filled in each hole by electro-plating or filling a metal paste. The filled metal finally becomes the conductive members that penetrate the silicon substrate, and ends thereof serve as mounting terminals to be connected to the circuit board.
A wiring layer is formed on the top surface of the silicon substrate after filling the metal in the holes. The conductive members in the holes of the silicon substrate and the electrode pads formed on the top surface of the wiring layer are electrically connected to each other through via holes or the like. The electrodes of the semiconductor device will be connected to the electrode pads.
After the wiring layer is formed on the top surface of the silicon substrate, ends of the conductive members in the holes of the silicon substrate are exposed by grinding (back-grinding) or etching the back surface of the silicon substrate. The back surface of the silicon substrate may be grinded until the ends of the conductive members in the holes of the silicon surface are grinded, and, thereafter, the ends of the conductive members are protruded by selectively etching only the silicon substrate. The thus-formed protruding ends serves as mounting terminals, and, thus, the semiconductor device mounted on the semiconductor device substrate (interposer) can be flip-chip mounted on the circuit board.
With the above-mentioned fabricating method of the interposer, it is necessary to form a plurality of deep cylindrical holes in a silicon substrate that are arranged in parallel with a small pitch. In order to form such deep holes in a silicon substrate, it is necessary to use a special dry etching method such as reactive ion etching (ICP-RIE). The reactive ion etching is not used in the usual semiconductor device production process (a process for fabricating a mounting substrates such as an interposer), and needs special and expensive apparatuses and processes. Therefore, the manufacturing cost of the semiconductor device substrate (interposer) will increase.
Moreover, the above-mentioned method needs the process for filling a metal in the deep holes in the silicon substrate. However, it is difficult to fill a metal in a deep hole without an air gap or an empty space, and a long process time is needed to fill a metal by plating.